Prior Art Statement
The following U.S. Letters Patent are representative of the most relevant prior art known to the Applicant at the time of filing the application:
______________________________________ 1,537,454 May 12, 1925 F. P Brock 1,893,117 January 3, 1933 D. E. Webster et al 1,924,748 August 29, 1933 E. E. Novotny et al 2,814,554 November 26, 1957 R. A. Rose 2,825,638 March 4, 1958 A. C. Booth 2,943,926 July 5, 1960 G. J. Goepfert 3,784,365 January 8, 1974 R. T. Caserta et al ______________________________________
U.S. Pat. No. 1,537,454 teaches the use of furfural as a solvent, plasticizer and supplemental hardener for phenolic binders for abrasive grains used in preparing grinding wheels. A few drops of creosote oil, phenol, or cresol are optionally used.
U.S. Pat. No. 1,893,117 describes the problem associated with the use of the highly reactive furfural, namely the agglomeration of the dry resin particles intended to coat the abrasive particles, referred to as "balling". A solution is presented in the use of Kolineum (.TM. Allied Chemical Corp.) which is a neutral anthracene oil coal tar fraction composed almost entirely of aromatic compounds. The process is a two-step one; first mixing the abrasive grains and resinoid powder with Kolineum and then adding the furfural.
U.S. Pat. No. 1,924,748 teaches the use of furfuryl alcohol or benzyl alcohol in place of furfuryl alcohol.
U.S. Pat. No. 2,814,554 provides a conventional example of using furfural in producing grinding wheels, and also shows the addition of anthracene oil as an anti dust agent after the abrasive grain and resin bond mix has been completely processed.
U.S. Pat. No. 2,825,638 shows employing a liquid rubber copolymer co-mingled with furfural that is used to wet an abrasive and phenolic mix to which cresol or creosote oil or guaicol is added in the mixer as a "pick-up agent" for the resin particles which have failed to attach themselves to the abrasive particles wetted with furfural in liquid rubber. It is stated that the "liquid pick-up agent" prevents balling.
U.S. Pat. No. 2,943,926 states that furfural is used with cresylic acid to form an initial coating of resin bond on the abrasive grains used to make a grinding wheel. A final step may include treating the resin coated grains with creosote oil and liquid resin, molding a wheel with the resulting mix and then curing the resin bond.
U.S. Pat. No. 3,784,365 shows the addition of fully chlorinated hydrocarbons to resinoid bond grinding wheels in addition to furfural and creosote oil.
Despite the many suggestions offered by the prior art for more efficiently mixing abrasive grains with powdered resin bond materials, the problems of balling and excessive dustiness still persist.
Prior art attempts to cure dustiness caused by the excess of dry resin powder which fails to adhere to the wetted abrasive particles have not been wholly satisfactory. The various reagents suggested in the prior art as dust depressants or pick-up agents introduce undesirable properties in the ultimate product such as the loss of uniformity reflected in lack of durability. Kolineum or creosote oil is a common agent for depressing dust, but in the amount needed to be effective, it is expensive and also introduces more oil into the abrasive than is desirable which degrades the grinding properties of the wheels. Phenol, cresol, etc., are too reactive to be satisfactory.
Another common problem is "balling", the tendency of the coated grains of abrasive particles to aggregate and form lumps when admixed with the resin. Balling is detrimental to the production of a mix having the desired uniformity of the grains in the resinoid bond material. Furfuryl alcohol has been suggested as an additive to prevent balling. However, furfuryl alcohol is a strong solvent, very reactive and easily polymerizes. Cresol, xylol, glycols, etc., which have also been suggested for this purpose and are also too reactive. Multi-step processing has also been employed to minimize balling, but this is time-consuming and expensive.